Usefulness of differential time to positivity between catheter and peripheral blood cultures for diagnosing catheter-related bloodstream infection: Data analysis from routine clinical practice in the intensive care unit

Purpose: To assess the accuracy of differential time to positivity (DTP) method for the diagnosis of catheter-related bloodstream infections (CRBSI) in the routine practice of our intensive care unit (ICU). Materials and methods: Over a five-year study period, ICU patients with a central venous catheter in place for ≥48 h and undergoing DTP test with catheter tip culture were analyzed. We investigated: the accuracy of DTP test with the usual threshold of 120 min in confirming the clinical suspicion of CRBSI; the most accurate threshold value of DTP to detect CRBSI; the diagnostic accuracy of the ratio (rather than the difference) between times to positivity. Results: Among 278 episodes of paired blood cultures, 13% were CRBSIs. DTP value ≥120 min used for the diagnosis of CRBSI yielded 41% sensitivity and 74% specificity. Performance of DTP values in predicting CRBSI was low (AUC = 0.60 [95%CI: 0.48-0.72]). Cutoff value of the ratio between times to positivity was 0.80, with 46% sensitivity and 79% specificity. Conclusions: The routine use of the DTP method at any cutoff point has inadequate accuracy in detecting CRBSI in the real every day clinical practice. Not even the ratio between times to positivity seems to be clinically useful.